Memorandum from Stan Nuffer, April 29, 1987

MEMORANDUM
CH2M Hill
TO: Interdisciplinary Team
FROM : Stan Nuffer
DATE: April 29, 1987
SUBJECT: Logan Canyon Environmental Study
PROJECT: B21163.FO
The twentieth Interdisciplinary Team Meeting was held on April 20, 1987, at 7:00 p.m. at the Forest Service District office in Logan, Utah. This meeting was followed by a day­long field trip in the canyon on April 21. Enclosed are the minutes for your review. Also attached for review is the Technical Memorandum on noise prepared by John Neil of UDOT.
The next meeting will be held on Monday, May 4, 1987, at 3:00 p.m. at the UDOT District office in Ogden, Utah. The agenda will be as follows:
1. Review minutes of April 20 and 21 meetings.
2. Discussion of the existing conditions portion of the socio-economic technical memorandum.
3. Discussion on spot improvement alternative.
4. Review of the noise technical memorandum by John Neil.
5. Wrap-up discussion of traffic projections.
Future meeting schedule:
May 27 - 3:00 p.m., District Office
June 27 - 3:00 p.m., Brigham City
SLC99/d.1901
LOGAN CANYON ENVIRONMENTAL STUDY
MINUTES OF ID TEAM MEETING
April 20, 1987
Attendance:
Arlo Waddops- Valley Engineering
Howard Richardson - UDOT
Lynn Zollinger - UDOT
Duncan Silver - FHWA
Clark Ostergarrd - USFS
Fred LaBar - USFS
Mark Shaw - USFS
John Wise, Herald Journal
Steve Flint - Audobon Society
Jack Spence - Utah Wilderness Society
Bill Helm -
Cliff Forsgren, CH2M HILL
Stan Nuffer, CH2M .HILL
ITEM 2 - REVIEW OF TRAFFIC FORECASTS
Cliff Forsgren reviewed a memo he had prepared that discussed forecast traffic volumes using annual data from 1940 through 1985 and population data for the same period. Two forecasting methods were discussed, the "past trends" and "population correlation" methods. Jack Spence indicated, that based upon the data he had seen, a linear function de­scribing past trends was probably as good as we were going to get using that method. He suggested that population and traffic be compared to see what kind of correlation, if any, could be established. If there is a reasonable correlation between population and traffic volume, the forecast will be used with past trends forecast to establish a range that future traffic is expected to fall within. Cliff will pre­pare some correlation comparisons for the team to consider.
ITEM 3 - REVIEW OF SCOPING COMMENTS
Stan Nuffer distributed summaries of the comments made at the scoping meetings and a partial summary of the written comments received. Duncan Silver pointed out that the number of people who commented on a specific issue was not as im­portant as the fact that the issue was raised. For that reason, the most important part of the summary was the table column headings that named the issues raised. Jack Spence
pointed out that big game was an issue that had been raised
1
MINUTES
INTERDISCIPLINARY TEAM FIELD TRIP
APRIL 21, 1987
Attendance:
Jim Naegle, UDOT
John Neil, UDOT
Howard Richardson, UDOT
Lynn Zollinger, UDOT
Fred LaBar, USFS
Mark Shaw, USFS
Richard Harris, USFS
Duncan Silver FHWA
Stan Nuffer, CH2M HILL
Cliff Forsgren, CH2M HILL
Arlo Waddups, Valley Engineers
Jack Spence, Sierra Club
Steve Flint, Audubon
Bill Helm
Tom Lyon
John Ellsworth
The team met at 8:00 a.m. at the F.S. District Ranger's office. Transportation for the field trip was in two vans provided by UDOT. Weather conditions for the trip were ideal.
Stop No.1 was at Lower Canyon M.P. 382.8 to consider the possibility of a slow vehicle turnout prior to the beginning of the study area. A slow vehicle turnout in this location would be marginal due to the curvature in the roadway and the limited sight distance back along the roadway.
Stop No.2 was at M.P. 384.0, or curve No.5 which is the first sharp curve encountered in the study section. Valley Engineering had previously marked the location of the center­line and the limit of the cut for both a 35 and 40 mph design. Red and white flagging marked the 35 mph centerline, yellow marked the 40 mph centerline, blue marked the 35 mph cut slope, and orange marked the 40 mph cut slope. The cut slopes had been staked for a 1/4:1 (horizontal to vertical) which assumed a rock cut. Both the 35 and 40 mph design results in the removal of the existing vegetation which would be difficult to re-establish on a 1/4:1 slope. A flatter slope could be considered to allow more revegetation.
Stop No.3 was at China Row, M.P. 385.35 and curve No.7. China Row is the location of a picnic area and also the tree canopy over the roadway formed primarily be black willows. The trees immediately adjacent to the road would be removed by any roadway widening or alignment improvement and would also be more greatly impacted by the 40 mph than the 35 mph design. The black willows are advanced in age and no secon­dary or replacement growth is apparent. If the canopy effect is to be maintained, replacement growth should be started that would conform to whatever alignment is selected. Because of the existing limited size of the picnic area, the Forest
1
Service would like to discourage its use. Curve No. 7 imme­diately upstream from China Row was marked for both 35 and 40 mph designs and a 1-1/2:1 cut slope. There was a differ­ence of opinion regarding the relative significance of the visual impact between the 35 and 40 mph designs.
Stop No.4 was at Logan Cave, M.P. 386.3 or curve No. 22. Any flattening of the curve to achieve 35 or 40 mph design speed would result in encroachment into the river. The ex­isting channel is already confined with haphazard unat­tractive riprap protecting the roadway. Several options for flattening the curve was discussed including the following:
1. Place the roadway on a bridge-type structure that would cantilever out over the river. The structure would extend out to about the center of the channel and would apply only to the 35 mph design. The roadway profile would have to be considerably higher than the existing roadway to provide hydraulic clearance beneath the cantilevers that would support the structure girders.· Clark Ostergaard showed an artists rendering of what the cantilever structure would look like.
2. Move the channel of the river by cutting into the bank opposite the roadway. This would require a channel change up to 500 feet in length for the 35 mph design speed and up to 600 feet for the 40 mph design speed. A retaining wall along the roadway would be included for both design speeds.
3. Retain the existing river channel and construct a bridge over the river for the roadway. This would require a structure up to 400 feet long for the 35 mph design speed and 550 feet long for the 40 mph design speed. The bridge would extend out to the center of the existing channel for the 35 mph design. For the 40 mph design the bridge would essentially cover the channel for about 300 feet. In both cases the roadway profile would be at least 4 feet higher than the existing roadway profile to provide for hydraulic clearance under the structure.
4. Switch the locations of the river and the roadway by constructing bridges at each end of the roadway curve. Due to the skew angle at which the roadway would cross the river, each of the bridges would be up to 200 feet in length. The bridges could be shortened by reducing the crossing skew angle by making some fairly sharp bends in the river at the structures.
2
The advantages and disadvantages of each of the four options was discussed, but no clear consensus was reached. It was agreed that additional studies should be done in this area to better define the options described above. The Forest Service would like to discourage parking immediately adjacent to the cave and provide parking near Cottonwood Creek.
Stop No.5 was at Cottonwood Creek and curve No. 24 at M.P. 386.45. The narrow structure should be replaced. At curve No. 24, the relative impacts of both the 35 and 40 mph designs were discussed. Both would result in considerable excavation into the hillside with the difference being in the amount of cut. An additional option identified in the field was to cut through the ridge that separates the Logan River and Cottonwood Creek drainages which would probably involve no more earthwork than the other options. It was agreed that it should be evaluated.
Stop No.6 was at M.P. 387.1 at curve No. 29. Both the 35 and 40 mph alignments were staked. The Hillside at this location is less vegetated and has no unusual or distin­guishing features. Little difference is evident between the 30 and 40 mph designs. The field inspection showed that it
would be desirable to have the 40 mph design align with the tangent to the west to eliminate the reverse curve.
Stop No. 7 was at M.P. 387.6 just below the lower twin bridge. It was concluded that the existing alignment should be fol­lowed to eliminate the need for additional fill, and if pos­sible to flatten the existing man-made rock fill slope so that it could be revegetated.
Stop No.8 was at M.P. 387.9 just above the lower twin bridge in the dugway. Replacement of the lower twin bridge was discussed and consensus was reached that the best option is to replace the bridge with a structure on new alignment up­stream of the existing bridge. This would require a new cut through the hill next to the existing cut, which could be filled and shaped to a naturally appearing contour with material from the new cut. At the other abutment it would be desirable to flatten the fill slopes, which would result in encroachment into the flats at the base of the fill.
In the dugway itself, the development of a climbing land was discussed which would require either a retaining wall on the downhill side or cutting further into the hillside. Clark Ostergaard showed an artists rendering of how a retaining wall would appear. Cutting into the hillside in the lower portion of the dugway does not appear feasible because the slope is less stable than the upper portion of the dugway where the existing rock cuts appear stable. The most feasi­ble solution may be a combination of widening the rock cut
3
in the upper portion of the dugway and constructing a retaining wall in the lower portion of the dugway.
Stop No. 9 was at M.P. 388.4 at the upper twin bridge. The most feasible location for replacement of the upper twin bridge would be down stream and as close to the existing bridge as possible to avoid the riparian areas of the river. The new bridge location would result in less shading of the structure which should alleviate some of the icing problems experienced by the existing structure.
Stop No. 10 was at M.P. 389.9 at Ricks Spring. There ap­peared to be consensus in shifting the alignment of the road as close to the river as possible to permit parking to be consolidated on the same side of the road as the spring.
Stop No. 11 was at M.P. 393.8 at Tony Grove Creek. The ex­isting narrow structure would need to be replaced. The road­way in this section could be widened to provide for a con­tinuous climbing lane with essentially all of the widening being done on the roadside away from the river.
Stop No. 12 was at the M.P. 396.9 at the lower Beaver Creek bridge near the Franklin Basin Road intersection. The ex­isting narrow structure would need to be replaced on the existing alignment. The Franklin Road intersection would also be improved.
Stop No. 13 was at M.P. 397.7 along Beaver Creek. Due to the relatively narrow area between Beaver Creek and the hill­side, it appeared to be difficult to develop a continuous climbing lane along Beaver Creek from just above the Franklin Road intersection to just below the Beaver Mountain Road intersection. Also the modified typical section should be considered for this 2.5 mile section.
Stop No. 14 was at M.P. 405.1 or Curve No. 85. Both the 35 and 40 mph designs would result in considerable new fill. The existing fill would need to be removed and used to re­store the cuts on either side of the fill to a more natural contour.
Stop No. 15 was at the Bear Lake Overlook at M.P. 405.8. The location of Alternative G-3 was pointed out, particularly the area where the deep cut through the ridge below the look­out would be located.
Stop No. 16 was back down the canyon at the Burnt Bridge at M.P. 385.7. The options for replacement of this bridge were discussed with the consensus being that the bridge should be replaced at the present location with a temporary bridge located downstream to carry traffic during construction.
4
Stop No. 17 was at M.P. 384.8 in the area just abbve Wood Camp campground where the McGuire Primrose is located. The plant was not yet readily apparent but the known locations were pointed out which extend westerly down the rock outcrop to within about 40 feet of the existing road. Any proposed road improvements should avoid this area. The potential location for a slow vehicle turnout at 389.9 should be far
enough upstream to not adversely affect this area.
SLC99/d.1902
5
LOGAN CANYON U.S. HIGHWAY 89
TECHNICAL MEMORANDUM
* * * NOISE * * *
Prepared By
John D.A. Neil, P.E.
UDOT
April 1987
Introduction
Acoustical Environment. Logan Canyon's acoustical (sound) environment has three parts - natural, human and mechanical. Natural sounds come from birds and other (usually small) denizens of the forest, rushing water, wind, and rustling leaves on trees. Human sounds in the
canyon include conversation, laughter and play, to name a few.
These first two parts of the acoustical environment together can be called background' noise, background sounds, or just simply the background. Whether or not the background is "noise" (unwanted sound) is according to one's own likes and dislikes.
Intruding into this background is a third part of the acoustical environment, namely noise from machinery. Included in this category for
Logan Canyon are such things as highway vehicles , off-road recreational vehicles, , overhead aircraft (usually high altitude and not a very
significant part of the soundscape), temporary construction activities and small power generators.
Sources of intruding noise studied in this report are restricted to those sources under some jurisdiction of the Utah . Department of Transportation - namely, highway traffic and highway construction.
Animals. It is common to assume for environmental reports that animals are not harmed, stressed, or annoyed any more than are humans by
highway traffic noise and construction noise related to highway improvements. This same assumption is made here.
Related to the above assumption is another - that animals are as adaptable to intruding noise as are humans. To date, no experience of this author suggests the contrary.
Scope of Study. No generally accepted research findings seem to be available that contradict the two assumptions just made. Consequently,
the major task of this report is simplified to accomplish the following: to understand and mInImIze noise impacts of highway improvement
alternatives affecting people using Logan Canyon.
Methodology
This noise study is consistent with Federal Highway Administration (FHWA) procedures and standards contained in its Federal-Aid Highway
Program Manual, Vol. 7, Chapter 7, Section 3 (FHPM 7-7-3), 1982 revision.
Traffic noise calculations and predictions are based - upon FHWA's Highway Traffic Noise Prediction Nomographs.
Noise levels used in this report are in terms of "Leq," representing "equivalent" (average) noise levels. Leq is a commonly used indicator of
general human sensitivity to traffic noise. Speech interference is particular ly vulnerable to noise, and speech relates well to the Leq
parameter.
Land Use and Sensitivity to Noise
Classification. The FHWA has classified human sensitivity to traffic noise into the following broad outdoor land use or activity categories, and has set a corresponding upper noise limit (or standard) for each category. These upper limits are used as criteria to determine when measures need to be considered to reduce noise.
In the following table is a general catalog of land uses adjacent to US-89 through Logan Canyon. Land uses, quantities and percentages shown
are estimates only; they are not intended to show an exact description of current usage, since change is expected as development continues in the canyon. Also shown in the table are corresponding FHWA activity categories and noise level criteria.
2
Senstive Developments. Activity category "8" developments are the land uses most likely to be sensitive to noise in Logan Canyon. Therefore, the remainder of this report only discusses these "B" activities.
Table 3 identifies many specific developments near enough to the highway to be noise sensitive. It is possible that more sites have been developed than are included on the list, and it is very likely that more sites will yet be developed. The noise criteria already discussed and
the noise predictions found later in this report may be generally applied. Consequently, it is hoped that architects and users of new developments utilize the results of this report to aid them in the design of new homes and recreation facilities in Logan Canyon.
Sites likely to be impacted. From Table 3, only two sites are likely to have some detrimental noise impact, resulting from changes in highway
alignment. These are both in Section 1:
China Row Campground
Lower Twin Bridge Picnic Area
Before studying these special sites, traffic noise in general will be analyzed.
Traffic Noise in Logan Canyon Generally
Affect of Level of Service and Volume. The combination of traffic volume and speed that give the most noise for Logan Canyon is not likely
to occur during " the peak traffic hour, when the road is utilized to near capacity (or "Level 0 f Service E"). Instead, the worst noise situation
usually occurs during periods of "Level of Service C" (LOS-C), which implies a situation of substantial traffic volume without severe restriction of speed and maneuverability.
4
Intuitively, this assertion seems reasonable when one recalls these two facts (assuming a road of fixed capacity): (1) that traffic volumes exceeding lOS-C cause congestion with a corresponding decrease in average vehicle speed; and (2) that noise is related to both volume and speed. It follows that a gain in noise from more vehicles is compensated by a noise loss from speed reduction. Thus, the maximum volume at LOS-C (also called the maximum service flow C or MSF -C) typically gives the worst noise scenario.
If improvements are made to increase the capacity of the road, then the MSF-C and corresponding maximum noise level also increase. However, it would take a doubling of volume to increase noise only 3 decibels (a barely noticeable increase).
MSF-C values for the three sections in logan Canyon have been documented in CH2M Hill's US-89 , Logan Canyon Study: Technical Memorandum (Draft, December 1986), pp. 6-12 and 6-17. They are as follows:
[see table 4]
Affect of Vehicle Type. The summer average weekday traffic composition includes approximately 84% passenger cats and light trucks (IT), according to the CH2M Hill study previously cited, p. 5-15. This is the least noisy class of vehicles (on a per vehicle basis).
Recreational vehicles (RV) and medium trucks (MT) are similar enough acoustically to be combined; these represent 13% of the traffic mix. The noise emission level of an average MT is about 11 decibels higher than the average car.
The remaining 3% of the vehicles are heavy trucks (HT); they are the noisiest class because they are typically diesel powered.
In the proportions indicated, the MT class as a whole contributes slightly more noise than ei ther the HT · or automobile class. This fact may have significance in the discussion of noise abatement.
Table 5 uses the traffic composition just described to portion the MSF-C traffic volumes from Table 4 into flow rates per vehicle type.
6
Affect of Speed. Noise is related to vehicle speed; and average vehicle speed is related to highway design (affecting level of service), vehicle type, and gradient. Table 6 (on the following page) gives the estimated average speeds for these three parameters.
Although the effects of speed on traffic noise are somewhat different for various vehicle types, approximate general effects may be condensed
into the following rule of thumb for Logan Canyon: for each 5 mph increment of average speed increase, the overall average noise level will
increase about 2 decibels.
Affect of Gradient. Climbing a grade takes extra power, and a byproduct of power is noise. Published research findings have shown that at normal highway speeds, only heavy trucks have a signi ficantly higher noise level on grades. F:HWA' s Highway Traffic Noise Prediction Model
(FHWA-RD-77-l08) suggests the following HT adjustments for uphill grades:
The FHWA makes no adjustment for downgrade direction. However, heavy trucks frequently use engine brakes, particularly on the steep grades in
7
Logan Canyon. Engine brake noise can vary considerably because of variations in engine and muffler design, load, speed, and driver. Consequently, the noise emission level for downhill trucks is not as predictable as is noise for uphill trucks. For simplicity in this report, it is assumed that heavy trucks in both directions emit noise that increase with gradient, according to the FHWA values given above.
Affect of Road Widening. Adding shoulders or widening traffic lanes symmetrically in both directions from the centerline of the Logan Canyon highway will not significantly change the noise level heard by a receiver who is farther than 25 feet from the centerline.
8
However, adding a passing lane to one side of the roadway will shift the noise in the direction of the passing lane. For receivers at a distance of 50 feet or less from the highway centerline, a passing lane (nearest the receiver) can add nearly 1 decibel to the overall Leq. This noise effect rapidly diminishes at increasing distances from the highway. At 100 feet there is essentially no noise increase.
According to Table 3, only one site is close enough to be affected by noise from a passing lane - China Row Campground. However, no passing lane is proposed for the vicinity of China Row; therefore road widening has no significant effect on noise for this project.
Noise Level Predictions. Traffic noise is related to the distance that a receiver is from the highway, as shown by the following chart. Affects of Level of Service, vehicle type, speed and gradient (previously discussed) are included in the approximate generalizations on the chart. Sound decays at a predictably uniform rate with increasing distance. For Logan Canyon vicinity the rate is estimated to be about 4.5 dB loss for each doubling of distance.
Unimproved road sections one and three are described best by Line C on the chart. Line C intersects the 67 dbA standard at a distance of 40
feet from the centerline. Any human activities farther than 40 feet will likely not exceed the standard if the ·adjacent road section does not exceed a 35 mph design.
Although Section Two (unimproved) is a high speed design, other factors in general reduce the noise to that of Line B. Any improvements
to Section Two will likely increase noise to Line A. Line A receivers need to be at least 75 feet away from the centerline in order to minimize
speech interference.
General Noise Impacts
There are three criteria that determine the severity impact: absolute level, relative increase, and fluctuation. All three are interrelated.
of noise
Absolute Level. Interference with speech is the basis for the standard or criterion level of 67 dBA. This criterion affects many human activities in the canyon.
China Row campground is near enough to the highway to be impacted by highway noise, especially if some highway improvement alternatives bring traffic somewhat closer to the campground.
All other developments seem to be at sufficient distance (greater than 75 feet) to not be seriously impacted by the average traffic noise level.
9
10
Relative Increase in Noise. Long term residents would be more likely to notice a traffic noise increase resulting from a highway improvement
than would seasonal residents, campers and other recreation oriented users of Logan Canyon. However, any change in traffic noise level in the
vicinity of permanently occupied homes is not likely to be noticed by the residents.
Many cabin dwellers at Bridger land Village (Section 3) may notice a drop in traffic noise, if the alignment is shifted from its present location. Generally, cabin dwellers will benefit acoustically from either of the two most feasible alternative alignments (F-3 to the north of the village, or G-3 to the south).
Fluctuation. Although the level of noise is higher in daytime than nighttime because of higher daytime use and daytime traffic in the canyon, heavy truck noise is more noticeable at night. This phenomenon is in part because there are less cars to partially mask the peak noise levels of the trucks. Consequently, the difference between highest noise peaks and background level are much more in contrast and therefore, noticeable at night.
This type of noise impact will generally affect residents and campers more than day-use recreationalists. So the people to benefit most are the ones who can be farthest from the traffic. Again, Bridgerland Village is a beneficiary of a change in highway alignment.
Special Problem Sites
China Row Campground. A shift in alignment of about 10 feet closer to the campground is one option being considered for highway improvement.
From the noise prediction chart on the preceding page, it can be seen that shortening the distance to the highway centerline from 70 feet to 60 feet will increase the noise level about 1 decibel to 64.5 dbA on Line C.
If highway improvements also ' cause the noise to raise from Line C to Line B (40 mph design), then the Leq will increase 2 additional decibels
to approximately 66.5 dBA.
Any highway improvements to a higher design speed than 40 mph (Line A) would have to consider noise abatement at this camp site.
Lower Twin Bridge Picnic Area. A shift in alignment of approximately 25 or 30 feet closer to the picnic area is being considered as part of a
new bridge and roadway alignment.
From the noise prediction chart on the preceding page, it can be seen that shortening the distance to the highway center line from 160 feet to
130 feet will normally (at grade) increase the noise level nearly 1.5 decibels from 58 to about 59.5 decibels on Line C.
However, the picnic area is at least 30 feet below the grade line of the highway. Thus, the picnic area is in an acoustical shadow zone, causing an approximate 7.5 db reduction of the Leq on the existing alignment to about 50.5 dBA.
11
Neglecting any vertical change in alignment, the horizontal shift will cause more of an acoustic shadow. The result would be a Leq of 59.5 - 9 (shadow) dB = 50.5 dBA approximately, which is the same Leq as for the existing alignment.
Thus, the Lower Twin Bridge Picnic Area will not be seriously impacted by tra ffic noise from any of the proposed improvements. Even with a change to Line A (worst noise situation), the predicted Leq will not exceed 63 dBA, which is below the 67 dBA standard.
In summary of noise impacts, . only China Row Campground may need to consider noise abatement, and this will be only in the case of greater than 40 mph design.
Noise Abatement
Noise abatement will not need to be planned into the project design for any location, regardless of the highway improvement options under
consideration, with one possible exception. China Row picnic area (one table) will need noise abatement consideration for a design speed of over 40 mph.
The feasibility of physical noise protection (wall or berm) at China Row is poor. A noise wall or berm would crowd the already very small picnic site, and would be likely out of character with the surrounding trees.
The most effective noise control is speed control at this location. Therefore, it is recommended that the design speed not exceed 40 mph at
this location.
Construction Noise
Construction is likely to occur on a piecemeal site-speci fic basis, beginning with bridge replacements and detour roads. Perhaps as early as
summer of 1988 if funds are available, a specific site improvement could get underway.
Acoustically, there is an advantage of this pattern of construction. People can still use the canyon in general for its diversified recreation and avoid noise from specific sites under construction.
Construction noise will probably be quite localized for two reasons. Sloped terrain and canyon walls will reflect the sound vertically and away from sensitive activities. · A few sites do have vertical cuts through rock which tend to channel sound horizontally; however, these sites are only found occasionally in the canyon, and fairly restricted to Section One.
The second reason why construction noise will probably be very localized is that there is an adequate amount of shielding from vegetation and natural topographic features to impede sound transmission.
12
Equipment used for construction will be very diversified to meet the needs of the various types of construction activities and in various types of terrain. Explosives and rock drills are expected to be used in various places. Standard precautions will be implemented to protect people from shock waves and noise.
All construction activities are subject to UDOT amended standard specification #107. 25 "Noise and Vibration Control."
Summary
Noise Abatement will not need to be planned into the project design for any location, regardless of the highway improvement options under
consideration, with one possible exception. China Row picnic area will need noise abatement consideration for a design speed of over 40 mph.
Because of the impracticality of physical noise barriers at China Row, it is recommended that the design speed not exceed 40 mph at this location.
No serious noise problem is expected from construction activities.
13
Noise loudness or intensity is measured in units called decibels, abbreviated dB or db. It is logarithmically based, so 10 decibels increase in sound intensity level means 10 times the acoustic energy from the source(s). However, human ears perceive the increase of 10 db as a doubling of loudness. The db scale covers the range of human hearing from 0 (the bottom limit of hearing ability for an average person with good hearing) to 130 (when sound energy causes pain to the ears). The following table relates noise levels associated with typical noise
sources. Typical human response and conversational problems are also given. Just as the human eye sees the color yellow best because it is in the center of the visible spectrum, so the human ear hears sounds better that are in the center of the human audio range of musical notes or pitches. Consequently" a weighting scale has been devised, and is internationally used in many sound measurements that tries to take this unequal human pitch perception into account. It is called the "A-weighted decibel scale" abbreviated "dbA," "dBA" or sometimes "dB(A)."
All sound measurements and predictions in this report use the standardized dBA.
APPENDIX TO LOGAN CANYON NOISE TECHNICAL MEMORANDUM
* * * SPEED ANALYSIS * * *
This Appendix is to determine approximate vehicle speeds throughout thp canyon for various scenarios. The results are for use in Table 6 (on page 8) of the Noise Technical Memorandum.
Advisory speed signs for specific curves are ignored for thee noise analysis. Average speed for sections of roadway under Level of Service C maximum flow is the target of thjs Appendix.
Each of the three main sections of subclassified into a typical gradient type gradient type as follows:
Section 1: Mountainous terrajn
a . Generally 2% average grade.
b. Twin Bridges locality 5.5% (approx.) average grade.
Section 2: Mostly rolling terrain 1 some mountainous
a . Generally 2% average grade.
h. Beaver Mtn. Road to UDOT Maintenance Camp, and MP-404 to summit1 4-7% grade (4.5% average).
Section 3: Mountainous terrain
a. Generally steep, to 7% (5.5% avg.).
b. Base of mountain to Garden City, 2% average grade, restricted speed. This is a relatively short section and can be ignored.
Existing Conditions
Since passing lanes are not provided anywhere in Logan Canyon above Right Hand Fork r it follows that cars must fall into queues behind heavy trucks and slow recreational vehiclesa (RV's) on uphill gradients. Since heavy trucks (HT) are the slowest class of vehicles on uphill grades, HT speed also is the limiting factor for all other vehicles on uphill grades.
The AASHTO 1/ Green Book" (A Policy on Geometric Design of Highways and Streets. 1984, p. 255) shows that HT on long grades steeper than 2% will travel about 20 mph.
For downhill and on grades less than 2%, it is assumed that all vehicles can go the speed consistent with level of service C, as determened [determined] by Table 8-1 and footnote b of the Highway Capacity Manual: TRB Special Report #209, p. 8-5:
Conclusion and Summary
For acoustical evaluation, speed nf vehicle classes have been calculated at LoS-C conditions for various design options. These speeds are compiled into Table 6 (p. 8) of the Technical Memorandum for Noise.
Average speed has been changed from directions given in footnote b in order to not exceed the design speed by more 5 mph.
Average speed of both directions of traffic for each section or subsectjon of roadway is sufficiently accurate to estimate noise levels. Consequently, the didirectional average speeds for existing conditions are calculated to be as follows:
Design Improvements
It is assumed for the noise study that all design improvement options will include at least some limited passing opportunities in all sections of the canyon. Consequently, heavy trucks no longer "would limit the speerd of faster vehicles totally.
The AASHTO Green Book, p . 258 shows that for long steep grades, RV's (and medium trucks assumed) cannot maintain a speed greater than 40 mph.
In the following table, as done for existing conditions, a bidirectiona] average speed is estimated for the given design speeds. Medium trucks and recreational vehicles are assumeed to have speeds between those of cars and heavy trucks .

Click tabs to swap between content that is broken into logical sections.

MEMORANDUM
CH2M Hill
TO: Interdisciplinary Team
FROM : Stan Nuffer
DATE: April 29, 1987
SUBJECT: Logan Canyon Environmental Study
PROJECT: B21163.FO
The twentieth Interdisciplinary Team Meeting was held on April 20, 1987, at 7:00 p.m. at the Forest Service District office in Logan, Utah. This meeting was followed by a day­long field trip in the canyon on April 21. Enclosed are the minutes for your review. Also attached for review is the Technical Memorandum on noise prepared by John Neil of UDOT.
The next meeting will be held on Monday, May 4, 1987, at 3:00 p.m. at the UDOT District office in Ogden, Utah. The agenda will be as follows:
1. Review minutes of April 20 and 21 meetings.
2. Discussion of the existing conditions portion of the socio-economic technical memorandum.
3. Discussion on spot improvement alternative.
4. Review of the noise technical memorandum by John Neil.
5. Wrap-up discussion of traffic projections.
Future meeting schedule:
May 27 - 3:00 p.m., District Office
June 27 - 3:00 p.m., Brigham City
SLC99/d.1901
LOGAN CANYON ENVIRONMENTAL STUDY
MINUTES OF ID TEAM MEETING
April 20, 1987
Attendance:
Arlo Waddops- Valley Engineering
Howard Richardson - UDOT
Lynn Zollinger - UDOT
Duncan Silver - FHWA
Clark Ostergarrd - USFS
Fred LaBar - USFS
Mark Shaw - USFS
John Wise, Herald Journal
Steve Flint - Audobon Society
Jack Spence - Utah Wilderness Society
Bill Helm -
Cliff Forsgren, CH2M HILL
Stan Nuffer, CH2M .HILL
ITEM 2 - REVIEW OF TRAFFIC FORECASTS
Cliff Forsgren reviewed a memo he had prepared that discussed forecast traffic volumes using annual data from 1940 through 1985 and population data for the same period. Two forecasting methods were discussed, the "past trends" and "population correlation" methods. Jack Spence indicated, that based upon the data he had seen, a linear function de­scribing past trends was probably as good as we were going to get using that method. He suggested that population and traffic be compared to see what kind of correlation, if any, could be established. If there is a reasonable correlation between population and traffic volume, the forecast will be used with past trends forecast to establish a range that future traffic is expected to fall within. Cliff will pre­pare some correlation comparisons for the team to consider.
ITEM 3 - REVIEW OF SCOPING COMMENTS
Stan Nuffer distributed summaries of the comments made at the scoping meetings and a partial summary of the written comments received. Duncan Silver pointed out that the number of people who commented on a specific issue was not as im­portant as the fact that the issue was raised. For that reason, the most important part of the summary was the table column headings that named the issues raised. Jack Spence
pointed out that big game was an issue that had been raised
1
MINUTES
INTERDISCIPLINARY TEAM FIELD TRIP
APRIL 21, 1987
Attendance:
Jim Naegle, UDOT
John Neil, UDOT
Howard Richardson, UDOT
Lynn Zollinger, UDOT
Fred LaBar, USFS
Mark Shaw, USFS
Richard Harris, USFS
Duncan Silver FHWA
Stan Nuffer, CH2M HILL
Cliff Forsgren, CH2M HILL
Arlo Waddups, Valley Engineers
Jack Spence, Sierra Club
Steve Flint, Audubon
Bill Helm
Tom Lyon
John Ellsworth
The team met at 8:00 a.m. at the F.S. District Ranger's office. Transportation for the field trip was in two vans provided by UDOT. Weather conditions for the trip were ideal.
Stop No.1 was at Lower Canyon M.P. 382.8 to consider the possibility of a slow vehicle turnout prior to the beginning of the study area. A slow vehicle turnout in this location would be marginal due to the curvature in the roadway and the limited sight distance back along the roadway.
Stop No.2 was at M.P. 384.0, or curve No.5 which is the first sharp curve encountered in the study section. Valley Engineering had previously marked the location of the center­line and the limit of the cut for both a 35 and 40 mph design. Red and white flagging marked the 35 mph centerline, yellow marked the 40 mph centerline, blue marked the 35 mph cut slope, and orange marked the 40 mph cut slope. The cut slopes had been staked for a 1/4:1 (horizontal to vertical) which assumed a rock cut. Both the 35 and 40 mph design results in the removal of the existing vegetation which would be difficult to re-establish on a 1/4:1 slope. A flatter slope could be considered to allow more revegetation.
Stop No.3 was at China Row, M.P. 385.35 and curve No.7. China Row is the location of a picnic area and also the tree canopy over the roadway formed primarily be black willows. The trees immediately adjacent to the road would be removed by any roadway widening or alignment improvement and would also be more greatly impacted by the 40 mph than the 35 mph design. The black willows are advanced in age and no secon­dary or replacement growth is apparent. If the canopy effect is to be maintained, replacement growth should be started that would conform to whatever alignment is selected. Because of the existing limited size of the picnic area, the Forest
1
Service would like to discourage its use. Curve No. 7 imme­diately upstream from China Row was marked for both 35 and 40 mph designs and a 1-1/2:1 cut slope. There was a differ­ence of opinion regarding the relative significance of the visual impact between the 35 and 40 mph designs.
Stop No.4 was at Logan Cave, M.P. 386.3 or curve No. 22. Any flattening of the curve to achieve 35 or 40 mph design speed would result in encroachment into the river. The ex­isting channel is already confined with haphazard unat­tractive riprap protecting the roadway. Several options for flattening the curve was discussed including the following:
1. Place the roadway on a bridge-type structure that would cantilever out over the river. The structure would extend out to about the center of the channel and would apply only to the 35 mph design. The roadway profile would have to be considerably higher than the existing roadway to provide hydraulic clearance beneath the cantilevers that would support the structure girders.· Clark Ostergaard showed an artists rendering of what the cantilever structure would look like.
2. Move the channel of the river by cutting into the bank opposite the roadway. This would require a channel change up to 500 feet in length for the 35 mph design speed and up to 600 feet for the 40 mph design speed. A retaining wall along the roadway would be included for both design speeds.
3. Retain the existing river channel and construct a bridge over the river for the roadway. This would require a structure up to 400 feet long for the 35 mph design speed and 550 feet long for the 40 mph design speed. The bridge would extend out to the center of the existing channel for the 35 mph design. For the 40 mph design the bridge would essentially cover the channel for about 300 feet. In both cases the roadway profile would be at least 4 feet higher than the existing roadway profile to provide for hydraulic clearance under the structure.
4. Switch the locations of the river and the roadway by constructing bridges at each end of the roadway curve. Due to the skew angle at which the roadway would cross the river, each of the bridges would be up to 200 feet in length. The bridges could be shortened by reducing the crossing skew angle by making some fairly sharp bends in the river at the structures.
2
The advantages and disadvantages of each of the four options was discussed, but no clear consensus was reached. It was agreed that additional studies should be done in this area to better define the options described above. The Forest Service would like to discourage parking immediately adjacent to the cave and provide parking near Cottonwood Creek.
Stop No.5 was at Cottonwood Creek and curve No. 24 at M.P. 386.45. The narrow structure should be replaced. At curve No. 24, the relative impacts of both the 35 and 40 mph designs were discussed. Both would result in considerable excavation into the hillside with the difference being in the amount of cut. An additional option identified in the field was to cut through the ridge that separates the Logan River and Cottonwood Creek drainages which would probably involve no more earthwork than the other options. It was agreed that it should be evaluated.
Stop No.6 was at M.P. 387.1 at curve No. 29. Both the 35 and 40 mph alignments were staked. The Hillside at this location is less vegetated and has no unusual or distin­guishing features. Little difference is evident between the 30 and 40 mph designs. The field inspection showed that it
would be desirable to have the 40 mph design align with the tangent to the west to eliminate the reverse curve.
Stop No. 7 was at M.P. 387.6 just below the lower twin bridge. It was concluded that the existing alignment should be fol­lowed to eliminate the need for additional fill, and if pos­sible to flatten the existing man-made rock fill slope so that it could be revegetated.
Stop No.8 was at M.P. 387.9 just above the lower twin bridge in the dugway. Replacement of the lower twin bridge was discussed and consensus was reached that the best option is to replace the bridge with a structure on new alignment up­stream of the existing bridge. This would require a new cut through the hill next to the existing cut, which could be filled and shaped to a naturally appearing contour with material from the new cut. At the other abutment it would be desirable to flatten the fill slopes, which would result in encroachment into the flats at the base of the fill.
In the dugway itself, the development of a climbing land was discussed which would require either a retaining wall on the downhill side or cutting further into the hillside. Clark Ostergaard showed an artists rendering of how a retaining wall would appear. Cutting into the hillside in the lower portion of the dugway does not appear feasible because the slope is less stable than the upper portion of the dugway where the existing rock cuts appear stable. The most feasi­ble solution may be a combination of widening the rock cut
3
in the upper portion of the dugway and constructing a retaining wall in the lower portion of the dugway.
Stop No. 9 was at M.P. 388.4 at the upper twin bridge. The most feasible location for replacement of the upper twin bridge would be down stream and as close to the existing bridge as possible to avoid the riparian areas of the river. The new bridge location would result in less shading of the structure which should alleviate some of the icing problems experienced by the existing structure.
Stop No. 10 was at M.P. 389.9 at Ricks Spring. There ap­peared to be consensus in shifting the alignment of the road as close to the river as possible to permit parking to be consolidated on the same side of the road as the spring.
Stop No. 11 was at M.P. 393.8 at Tony Grove Creek. The ex­isting narrow structure would need to be replaced. The road­way in this section could be widened to provide for a con­tinuous climbing lane with essentially all of the widening being done on the roadside away from the river.
Stop No. 12 was at the M.P. 396.9 at the lower Beaver Creek bridge near the Franklin Basin Road intersection. The ex­isting narrow structure would need to be replaced on the existing alignment. The Franklin Road intersection would also be improved.
Stop No. 13 was at M.P. 397.7 along Beaver Creek. Due to the relatively narrow area between Beaver Creek and the hill­side, it appeared to be difficult to develop a continuous climbing lane along Beaver Creek from just above the Franklin Road intersection to just below the Beaver Mountain Road intersection. Also the modified typical section should be considered for this 2.5 mile section.
Stop No. 14 was at M.P. 405.1 or Curve No. 85. Both the 35 and 40 mph designs would result in considerable new fill. The existing fill would need to be removed and used to re­store the cuts on either side of the fill to a more natural contour.
Stop No. 15 was at the Bear Lake Overlook at M.P. 405.8. The location of Alternative G-3 was pointed out, particularly the area where the deep cut through the ridge below the look­out would be located.
Stop No. 16 was back down the canyon at the Burnt Bridge at M.P. 385.7. The options for replacement of this bridge were discussed with the consensus being that the bridge should be replaced at the present location with a temporary bridge located downstream to carry traffic during construction.
4
Stop No. 17 was at M.P. 384.8 in the area just abbve Wood Camp campground where the McGuire Primrose is located. The plant was not yet readily apparent but the known locations were pointed out which extend westerly down the rock outcrop to within about 40 feet of the existing road. Any proposed road improvements should avoid this area. The potential location for a slow vehicle turnout at 389.9 should be far
enough upstream to not adversely affect this area.
SLC99/d.1902
5
LOGAN CANYON U.S. HIGHWAY 89
TECHNICAL MEMORANDUM
* * * NOISE * * *
Prepared By
John D.A. Neil, P.E.
UDOT
April 1987
Introduction
Acoustical Environment. Logan Canyon's acoustical (sound) environment has three parts - natural, human and mechanical. Natural sounds come from birds and other (usually small) denizens of the forest, rushing water, wind, and rustling leaves on trees. Human sounds in the
canyon include conversation, laughter and play, to name a few.
These first two parts of the acoustical environment together can be called background' noise, background sounds, or just simply the background. Whether or not the background is "noise" (unwanted sound) is according to one's own likes and dislikes.
Intruding into this background is a third part of the acoustical environment, namely noise from machinery. Included in this category for
Logan Canyon are such things as highway vehicles , off-road recreational vehicles, , overhead aircraft (usually high altitude and not a very
significant part of the soundscape), temporary construction activities and small power generators.
Sources of intruding noise studied in this report are restricted to those sources under some jurisdiction of the Utah . Department of Transportation - namely, highway traffic and highway construction.
Animals. It is common to assume for environmental reports that animals are not harmed, stressed, or annoyed any more than are humans by
highway traffic noise and construction noise related to highway improvements. This same assumption is made here.
Related to the above assumption is another - that animals are as adaptable to intruding noise as are humans. To date, no experience of this author suggests the contrary.
Scope of Study. No generally accepted research findings seem to be available that contradict the two assumptions just made. Consequently,
the major task of this report is simplified to accomplish the following: to understand and mInImIze noise impacts of highway improvement
alternatives affecting people using Logan Canyon.
Methodology
This noise study is consistent with Federal Highway Administration (FHWA) procedures and standards contained in its Federal-Aid Highway
Program Manual, Vol. 7, Chapter 7, Section 3 (FHPM 7-7-3), 1982 revision.
Traffic noise calculations and predictions are based - upon FHWA's Highway Traffic Noise Prediction Nomographs.
Noise levels used in this report are in terms of "Leq," representing "equivalent" (average) noise levels. Leq is a commonly used indicator of
general human sensitivity to traffic noise. Speech interference is particular ly vulnerable to noise, and speech relates well to the Leq
parameter.
Land Use and Sensitivity to Noise
Classification. The FHWA has classified human sensitivity to traffic noise into the following broad outdoor land use or activity categories, and has set a corresponding upper noise limit (or standard) for each category. These upper limits are used as criteria to determine when measures need to be considered to reduce noise.
In the following table is a general catalog of land uses adjacent to US-89 through Logan Canyon. Land uses, quantities and percentages shown
are estimates only; they are not intended to show an exact description of current usage, since change is expected as development continues in the canyon. Also shown in the table are corresponding FHWA activity categories and noise level criteria.
2
Senstive Developments. Activity category "8" developments are the land uses most likely to be sensitive to noise in Logan Canyon. Therefore, the remainder of this report only discusses these "B" activities.
Table 3 identifies many specific developments near enough to the highway to be noise sensitive. It is possible that more sites have been developed than are included on the list, and it is very likely that more sites will yet be developed. The noise criteria already discussed and
the noise predictions found later in this report may be generally applied. Consequently, it is hoped that architects and users of new developments utilize the results of this report to aid them in the design of new homes and recreation facilities in Logan Canyon.
Sites likely to be impacted. From Table 3, only two sites are likely to have some detrimental noise impact, resulting from changes in highway
alignment. These are both in Section 1:
China Row Campground
Lower Twin Bridge Picnic Area
Before studying these special sites, traffic noise in general will be analyzed.
Traffic Noise in Logan Canyon Generally
Affect of Level of Service and Volume. The combination of traffic volume and speed that give the most noise for Logan Canyon is not likely
to occur during " the peak traffic hour, when the road is utilized to near capacity (or "Level 0 f Service E"). Instead, the worst noise situation
usually occurs during periods of "Level of Service C" (LOS-C), which implies a situation of substantial traffic volume without severe restriction of speed and maneuverability.
4
Intuitively, this assertion seems reasonable when one recalls these two facts (assuming a road of fixed capacity): (1) that traffic volumes exceeding lOS-C cause congestion with a corresponding decrease in average vehicle speed; and (2) that noise is related to both volume and speed. It follows that a gain in noise from more vehicles is compensated by a noise loss from speed reduction. Thus, the maximum volume at LOS-C (also called the maximum service flow C or MSF -C) typically gives the worst noise scenario.
If improvements are made to increase the capacity of the road, then the MSF-C and corresponding maximum noise level also increase. However, it would take a doubling of volume to increase noise only 3 decibels (a barely noticeable increase).
MSF-C values for the three sections in logan Canyon have been documented in CH2M Hill's US-89 , Logan Canyon Study: Technical Memorandum (Draft, December 1986), pp. 6-12 and 6-17. They are as follows:
[see table 4]
Affect of Vehicle Type. The summer average weekday traffic composition includes approximately 84% passenger cats and light trucks (IT), according to the CH2M Hill study previously cited, p. 5-15. This is the least noisy class of vehicles (on a per vehicle basis).
Recreational vehicles (RV) and medium trucks (MT) are similar enough acoustically to be combined; these represent 13% of the traffic mix. The noise emission level of an average MT is about 11 decibels higher than the average car.
The remaining 3% of the vehicles are heavy trucks (HT); they are the noisiest class because they are typically diesel powered.
In the proportions indicated, the MT class as a whole contributes slightly more noise than ei ther the HT · or automobile class. This fact may have significance in the discussion of noise abatement.
Table 5 uses the traffic composition just described to portion the MSF-C traffic volumes from Table 4 into flow rates per vehicle type.
6
Affect of Speed. Noise is related to vehicle speed; and average vehicle speed is related to highway design (affecting level of service), vehicle type, and gradient. Table 6 (on the following page) gives the estimated average speeds for these three parameters.
Although the effects of speed on traffic noise are somewhat different for various vehicle types, approximate general effects may be condensed
into the following rule of thumb for Logan Canyon: for each 5 mph increment of average speed increase, the overall average noise level will
increase about 2 decibels.
Affect of Gradient. Climbing a grade takes extra power, and a byproduct of power is noise. Published research findings have shown that at normal highway speeds, only heavy trucks have a signi ficantly higher noise level on grades. F:HWA' s Highway Traffic Noise Prediction Model
(FHWA-RD-77-l08) suggests the following HT adjustments for uphill grades:
The FHWA makes no adjustment for downgrade direction. However, heavy trucks frequently use engine brakes, particularly on the steep grades in
7
Logan Canyon. Engine brake noise can vary considerably because of variations in engine and muffler design, load, speed, and driver. Consequently, the noise emission level for downhill trucks is not as predictable as is noise for uphill trucks. For simplicity in this report, it is assumed that heavy trucks in both directions emit noise that increase with gradient, according to the FHWA values given above.
Affect of Road Widening. Adding shoulders or widening traffic lanes symmetrically in both directions from the centerline of the Logan Canyon highway will not significantly change the noise level heard by a receiver who is farther than 25 feet from the centerline.
8
However, adding a passing lane to one side of the roadway will shift the noise in the direction of the passing lane. For receivers at a distance of 50 feet or less from the highway centerline, a passing lane (nearest the receiver) can add nearly 1 decibel to the overall Leq. This noise effect rapidly diminishes at increasing distances from the highway. At 100 feet there is essentially no noise increase.
According to Table 3, only one site is close enough to be affected by noise from a passing lane - China Row Campground. However, no passing lane is proposed for the vicinity of China Row; therefore road widening has no significant effect on noise for this project.
Noise Level Predictions. Traffic noise is related to the distance that a receiver is from the highway, as shown by the following chart. Affects of Level of Service, vehicle type, speed and gradient (previously discussed) are included in the approximate generalizations on the chart. Sound decays at a predictably uniform rate with increasing distance. For Logan Canyon vicinity the rate is estimated to be about 4.5 dB loss for each doubling of distance.
Unimproved road sections one and three are described best by Line C on the chart. Line C intersects the 67 dbA standard at a distance of 40
feet from the centerline. Any human activities farther than 40 feet will likely not exceed the standard if the ·adjacent road section does not exceed a 35 mph design.
Although Section Two (unimproved) is a high speed design, other factors in general reduce the noise to that of Line B. Any improvements
to Section Two will likely increase noise to Line A. Line A receivers need to be at least 75 feet away from the centerline in order to minimize
speech interference.
General Noise Impacts
There are three criteria that determine the severity impact: absolute level, relative increase, and fluctuation. All three are interrelated.
of noise
Absolute Level. Interference with speech is the basis for the standard or criterion level of 67 dBA. This criterion affects many human activities in the canyon.
China Row campground is near enough to the highway to be impacted by highway noise, especially if some highway improvement alternatives bring traffic somewhat closer to the campground.
All other developments seem to be at sufficient distance (greater than 75 feet) to not be seriously impacted by the average traffic noise level.
9
10
Relative Increase in Noise. Long term residents would be more likely to notice a traffic noise increase resulting from a highway improvement
than would seasonal residents, campers and other recreation oriented users of Logan Canyon. However, any change in traffic noise level in the
vicinity of permanently occupied homes is not likely to be noticed by the residents.
Many cabin dwellers at Bridger land Village (Section 3) may notice a drop in traffic noise, if the alignment is shifted from its present location. Generally, cabin dwellers will benefit acoustically from either of the two most feasible alternative alignments (F-3 to the north of the village, or G-3 to the south).
Fluctuation. Although the level of noise is higher in daytime than nighttime because of higher daytime use and daytime traffic in the canyon, heavy truck noise is more noticeable at night. This phenomenon is in part because there are less cars to partially mask the peak noise levels of the trucks. Consequently, the difference between highest noise peaks and background level are much more in contrast and therefore, noticeable at night.
This type of noise impact will generally affect residents and campers more than day-use recreationalists. So the people to benefit most are the ones who can be farthest from the traffic. Again, Bridgerland Village is a beneficiary of a change in highway alignment.
Special Problem Sites
China Row Campground. A shift in alignment of about 10 feet closer to the campground is one option being considered for highway improvement.
From the noise prediction chart on the preceding page, it can be seen that shortening the distance to the highway centerline from 70 feet to 60 feet will increase the noise level about 1 decibel to 64.5 dbA on Line C.
If highway improvements also ' cause the noise to raise from Line C to Line B (40 mph design), then the Leq will increase 2 additional decibels
to approximately 66.5 dBA.
Any highway improvements to a higher design speed than 40 mph (Line A) would have to consider noise abatement at this camp site.
Lower Twin Bridge Picnic Area. A shift in alignment of approximately 25 or 30 feet closer to the picnic area is being considered as part of a
new bridge and roadway alignment.
From the noise prediction chart on the preceding page, it can be seen that shortening the distance to the highway center line from 160 feet to
130 feet will normally (at grade) increase the noise level nearly 1.5 decibels from 58 to about 59.5 decibels on Line C.
However, the picnic area is at least 30 feet below the grade line of the highway. Thus, the picnic area is in an acoustical shadow zone, causing an approximate 7.5 db reduction of the Leq on the existing alignment to about 50.5 dBA.
11
Neglecting any vertical change in alignment, the horizontal shift will cause more of an acoustic shadow. The result would be a Leq of 59.5 - 9 (shadow) dB = 50.5 dBA approximately, which is the same Leq as for the existing alignment.
Thus, the Lower Twin Bridge Picnic Area will not be seriously impacted by tra ffic noise from any of the proposed improvements. Even with a change to Line A (worst noise situation), the predicted Leq will not exceed 63 dBA, which is below the 67 dBA standard.
In summary of noise impacts, . only China Row Campground may need to consider noise abatement, and this will be only in the case of greater than 40 mph design.
Noise Abatement
Noise abatement will not need to be planned into the project design for any location, regardless of the highway improvement options under
consideration, with one possible exception. China Row picnic area (one table) will need noise abatement consideration for a design speed of over 40 mph.
The feasibility of physical noise protection (wall or berm) at China Row is poor. A noise wall or berm would crowd the already very small picnic site, and would be likely out of character with the surrounding trees.
The most effective noise control is speed control at this location. Therefore, it is recommended that the design speed not exceed 40 mph at
this location.
Construction Noise
Construction is likely to occur on a piecemeal site-speci fic basis, beginning with bridge replacements and detour roads. Perhaps as early as
summer of 1988 if funds are available, a specific site improvement could get underway.
Acoustically, there is an advantage of this pattern of construction. People can still use the canyon in general for its diversified recreation and avoid noise from specific sites under construction.
Construction noise will probably be quite localized for two reasons. Sloped terrain and canyon walls will reflect the sound vertically and away from sensitive activities. · A few sites do have vertical cuts through rock which tend to channel sound horizontally; however, these sites are only found occasionally in the canyon, and fairly restricted to Section One.
The second reason why construction noise will probably be very localized is that there is an adequate amount of shielding from vegetation and natural topographic features to impede sound transmission.
12
Equipment used for construction will be very diversified to meet the needs of the various types of construction activities and in various types of terrain. Explosives and rock drills are expected to be used in various places. Standard precautions will be implemented to protect people from shock waves and noise.
All construction activities are subject to UDOT amended standard specification #107. 25 "Noise and Vibration Control."
Summary
Noise Abatement will not need to be planned into the project design for any location, regardless of the highway improvement options under
consideration, with one possible exception. China Row picnic area will need noise abatement consideration for a design speed of over 40 mph.
Because of the impracticality of physical noise barriers at China Row, it is recommended that the design speed not exceed 40 mph at this location.
No serious noise problem is expected from construction activities.
13
Noise loudness or intensity is measured in units called decibels, abbreviated dB or db. It is logarithmically based, so 10 decibels increase in sound intensity level means 10 times the acoustic energy from the source(s). However, human ears perceive the increase of 10 db as a doubling of loudness. The db scale covers the range of human hearing from 0 (the bottom limit of hearing ability for an average person with good hearing) to 130 (when sound energy causes pain to the ears). The following table relates noise levels associated with typical noise
sources. Typical human response and conversational problems are also given. Just as the human eye sees the color yellow best because it is in the center of the visible spectrum, so the human ear hears sounds better that are in the center of the human audio range of musical notes or pitches. Consequently" a weighting scale has been devised, and is internationally used in many sound measurements that tries to take this unequal human pitch perception into account. It is called the "A-weighted decibel scale" abbreviated "dbA," "dBA" or sometimes "dB(A)."
All sound measurements and predictions in this report use the standardized dBA.
APPENDIX TO LOGAN CANYON NOISE TECHNICAL MEMORANDUM
* * * SPEED ANALYSIS * * *
This Appendix is to determine approximate vehicle speeds throughout thp canyon for various scenarios. The results are for use in Table 6 (on page 8) of the Noise Technical Memorandum.
Advisory speed signs for specific curves are ignored for thee noise analysis. Average speed for sections of roadway under Level of Service C maximum flow is the target of thjs Appendix.
Each of the three main sections of subclassified into a typical gradient type gradient type as follows:
Section 1: Mountainous terrajn
a . Generally 2% average grade.
b. Twin Bridges locality 5.5% (approx.) average grade.
Section 2: Mostly rolling terrain 1 some mountainous
a . Generally 2% average grade.
h. Beaver Mtn. Road to UDOT Maintenance Camp, and MP-404 to summit1 4-7% grade (4.5% average).
Section 3: Mountainous terrain
a. Generally steep, to 7% (5.5% avg.).
b. Base of mountain to Garden City, 2% average grade, restricted speed. This is a relatively short section and can be ignored.
Existing Conditions
Since passing lanes are not provided anywhere in Logan Canyon above Right Hand Fork r it follows that cars must fall into queues behind heavy trucks and slow recreational vehiclesa (RV's) on uphill gradients. Since heavy trucks (HT) are the slowest class of vehicles on uphill grades, HT speed also is the limiting factor for all other vehicles on uphill grades.
The AASHTO 1/ Green Book" (A Policy on Geometric Design of Highways and Streets. 1984, p. 255) shows that HT on long grades steeper than 2% will travel about 20 mph.
For downhill and on grades less than 2%, it is assumed that all vehicles can go the speed consistent with level of service C, as determened [determined] by Table 8-1 and footnote b of the Highway Capacity Manual: TRB Special Report #209, p. 8-5:
Conclusion and Summary
For acoustical evaluation, speed nf vehicle classes have been calculated at LoS-C conditions for various design options. These speeds are compiled into Table 6 (p. 8) of the Technical Memorandum for Noise.
Average speed has been changed from directions given in footnote b in order to not exceed the design speed by more 5 mph.
Average speed of both directions of traffic for each section or subsectjon of roadway is sufficiently accurate to estimate noise levels. Consequently, the didirectional average speeds for existing conditions are calculated to be as follows:
Design Improvements
It is assumed for the noise study that all design improvement options will include at least some limited passing opportunities in all sections of the canyon. Consequently, heavy trucks no longer "would limit the speerd of faster vehicles totally.
The AASHTO Green Book, p . 258 shows that for long steep grades, RV's (and medium trucks assumed) cannot maintain a speed greater than 40 mph.
In the following table, as done for existing conditions, a bidirectiona] average speed is estimated for the given design speeds. Medium trucks and recreational vehicles are assumeed to have speeds between those of cars and heavy trucks .